Presently, power control in cellular communication systems is handled in a reactive manner. First, power measurements are made of the received signal at a present time. A power adjustment command is then sent to adjust the transmitter power moving it toward some threshold value. Because of transmission delays, the adjustment is actually made at a future time. If the received power is in the process of changing between the present time, at which the measurement is taken, and the future time, when the power adjustment is implemented, the adjustment based upon present time measurements can result in over adjustment.
By way of example, we will use the situation where the transmitter is a mobile subscriber moving toward a base station. As the mobile proceeds toward the base station, the received signal power measured at the base station will increase, assuming that the mobile output power is fixed. If the received power is measured as low at the present time, the base station will direct the mobile to increase its power. However, since the mobile is moving toward the base station, the receive power will be increasing anyway. At points where the power is close to a maximum threshold, the directed increase, combined with the increase due to the movement of the mobile, will result in the receive power being pushed past the maximum threshold.
Because there is a time delay between the power measurement time and the power adjustment time, any previous power adjustments executed during this period also cause unwanted results. The effect of this delay is illustrated by the fact that the power measurement is made at time t.sub.0. A power adjustment command, based upon the t.sub.0 measurement, is then sent which reaches the subscriber at some time t.sub.x. In the interim between t.sub.0 and t.sub.x, the subscriber has received and implemented other adjustment commands. Thus the power adjustment command based upon the t.sub.0 is often the incorrect adjustment for the actual power at t.sub.x.